The invention pertains to methods of reducing NOx and apparatuses for reducing NOx.
A wide variety of technology exists that is aimed at reducing NOx, wherein x is greater than zero, in emission sources. As emission limits decrease and cost reductions are desired, new NOx emission control methods are being evaluated. One emission source identified for improved NOx reduction includes lean burn spark and compression ignition engine exhaust. One example of such an emission source includes diesel engines.
A desire exists to improve NOx reduction for emission sources including, but not limited to, diesel engines.
In one aspect of the invention, a NOx reduction method includes treating a first gas containing NOx, wherein x is greater than zero, and producing a second gas containing NO2. A portion of the NO2 in the second gas can be reduced to N2 and a third gas produced containing less NOx than the first gas, substantially all of the third gas NOx being NO. The third gas can be treated and a fourth gas produced containing NO2. A portion of the NO2 in the fourth gas can be reduced to N2 and a fifth gas produced containing less NOx than the third gas, substantially all of the fifth gas NOx being NO. As one example, a fraction of the first gas NOx treated to second gas NO2 can approximately equal a fraction of the third gas NOx treated to fourth gas NO2. Also, the portion of the second gas NO2 reduced can be less than about 70 volume percent (vol %).
In another aspect of the invention, a NOx reduction method includes treating a first gas containing NOx, wherein x is greater than zero, with a first plasma and producing a second gas containing NO2. The method includes reducing a portion of the NO2 in the second gas to N2 with a first catalyst and producing a third gas containing less NOx than the first gas, substantially all of the third gas NOx being NO. The third gas containing NOx can be treated with a second plasma and a fourth gas produced containing NO2. A portion of the NO2 in the fourth gas can be reduced to N2 with a second catalyst and a fifth gas produced containing less NOx than the third gas. As an example, the first and third gases can further contain hydrocarbon. Treating the first gas and reducing a portion of the NO2 in the second gas can provide oxidation of less than 50 vol % of the hydrocarbon in the first gas. Treating the third gas and reducing a portion of the NO2 in the fourth gas can provide oxidation of less than 50 vol % of the hydrocarbon in the third gas. The method can further include controlling energy consumption of the first and second plasmas independent of each other. A combined energy consumption of the first and second plasmas can be substantially minimized.
In yet another aspect of the invention, a NOx reduction method can include performing a step at least three times in series. The step includes converting NOx, wherein x is greater than zero, comprised by an inlet gas to NO2 with a plasma and catalytically reducing NO2 at least to N2 and NO comprised by an outlet gas. The at least three performances of the step can be operated to plasma convert approximately equal fractions of the inlet gas NOx to NO2. As an example, the outlet gas of at least two of the three performances of the step can comprise the inlet gas for a subsequent performance of the step.
In a further aspect of the invention, a NOx reduction apparatus includes a plurality of reactor units in series. Individual reactor units include a plasma device and a reducing catalyst. The plasma device exhibits the property of converting NOx, wherein x is greater than zero, to NO2. The reducing catalyst exhibits the property of reducing NO2 to a reaction product consisting essentially of N2 and NO. The apparatus can further include a plurality of separate power control devices for respective plasma devices of individual reactor units. The plasma devices can include dual dielectric barrier discharge devices. The reducing catalysts can include at least one of barium zeolite Y type (Baxe2x80x94Y) and sodium zeolite Y type (Naxe2x80x94Y).